The present invention relates to an apparatus for inspecting a temperature sensor disposed in an exhaust system of an internal combustion engine.
The ability of a catalyst of a catalytic converter installed in an exhaust system of a vehicle may decrease if the catalytic converter is exposed to an abnormally high temperature. In order to control the temperature of the catalyst, a temperature sensor is usually disposed in the vicinity of the catalyst. This temperature sensor generally uses a thermistor having lower resistance at higher temperature. The value of resistance becomes larger as the temperature becomes lower.
The Japanese Patent Application Publication No. S59-120835 discloses a technique for detecting breaking of a temperature sensor by providing a second reference power supply for generating a second voltage signal different from a voltage signal from the temperature sensor at a normal time. The second voltage signal is compared with the voltage signal from the temperature sensor.
In case of a diesel engine, the temperature of the exhaust gas is relatively low. If an inspection for a temperature sensor is performed under a condition that a temperature of an exhaust system is low, for example, immediately after the engine starts, the sensor may produce a fixed output value due to the low temperature even if the temperature sensor is normal, which may lead to a wrong detection that the sensor is in a failure.
Thus, there is a need for a temperature sensor inspecting technique that does not produce a wrong detection.